Abstract The oxidation of 1-pentene and the effect of nitric oxide (NO) on this oxidation has been examined in a pressurized flow reactor facility. The experiments were conducted at 6 atmospheres over the temperature range of 600–800 K and an equivalence ratio of 0.4. 1-Pentene showed alkane type behavior exhibiting low temperature reactivity and strong negative temperature coefficient behavior. An examination of stable species composition revealed that hydrogen abstraction reactions leading to allyl radicals are more important than radical addition to the double bond. This is in contrast to previous studies on terminal olefins where the addition route was proposed as the dominant fuel consumption pathway. We believe that as carbon number of the terminal olefin increases alkane type reaction behavior occurs at the other end of the molecule and this is the reactivity observed under our experimental conditions. The presence of small concentrations of nitric oxide (0–500 ppm mole fraction) significantly altered 1-pentene oxidation at these temperatures. The effect of NO is a result of the competion between its promoting effect through reaction with HO 2 · radicals and its retarding effect through reaction with OH · radicals. Thus the effect depends strongly on the underlying fuel oxidation chemistry which generates the HO 2 · and OH · radicals and the concentration of the nitric oxide added. An explanation for this behavior is presented in the paper.